A long-range goal of the proposed research is to identify novel and effective therapeutic approaches for the treatment of relapsed or refractory B cell non-Hodgkin's lymphoma (B-NHL). Despite recent advances (i.e. incorporation of rituximab) in the design of treatment for B-NHL, greater than half of previously treated patients subsequently demonstrate therapy-resistant disease at the time of relapse. The specific aims of the proposed research seek to understand the mechanism(s)-of-action of bortezomib (Velcade), a proteasome inhibitor that has shown recent promise in the treatment of therapy-resistant B cell malignancies. The precise mechanism(s)-of-action of bortezomib remains largely undefined, but in many cases likely involves the induction of cell death via apoptosis. Preliminary data indicate that bortezomib is effective at killing several chemotherapy-resistant aggressive B-NHL cell lines, as well as in patient lymphoma specimens. Interestingly, bortezomib demonstrates the capacity to engage several molecular pathways to promote cell death. In the first specific aim, a role for apoptosis and the Bcl-2 family of proteins in regulating bortezomib-mediated cell death of therapy resistant B-NHL will be investigated. In the second aim, a potential role for two additional modes of cell death, autophagy and necrosis, will be explored. The results obtained from this aim are expected to be of particular interest, as targeting non-apoptotic mechanisms of cell death are just beginning to be considered therapeutically. Finally, in aim 3, we will apply the knowledge gained from the laboratory studies to further delineate bortezomib's therapeutic efficacy and validate its mechanism(s)-of-action in primary lymphoma samples. Each refractory/resistant lymphoma will be categorized by DNA microarray (Collaborator: L. Staudt, NIH) as having an activated B cell (ABC), a germinal center B cell (GCB), or other genotype. This will allow direct comparison of each unique proteasome's activity, both ex vivo and (with bortezomib) clinically, between DLBCLs with poor prognosis (ABC) versus those with generally better outcomes (GCB). Preliminary data from a recently completed Phase II NCI Velcade-EPOCH clinical trial (PI: W. Wilson, NCI; Co-investigator: M. Czuczman, RPCI) in patients with relapsed/refractory B-cell NHL indicates that bortezomib increased EPOCH's anti-tumor activity primarily in the poor prognosis ABC subgroup secondary to its ability to down- modulate NF:B activity and lead to an increased pro-apoptotic potential in lymphoma cells. Collectively, the proposed studies are designed to reveal detailed mechanism(s)-of-action of bortezomib in the context of overcoming therapy-resistant B-NHL, and concurrently developing an effective, less toxic, novel immunochemotherapeutic salvage regimen (i.e. VDR) for patients with relapsed/refractory DLBCL. To strengthen our original submission, we have identified three next-generation proteasome inhibitors with unique mechanisms-of-action which we will include into our experimental design. Our research findings will be utilized in the development of future evidence-based proteasome inhibitor-associated therapies for B-cell lymphomas.